Network Working Group D. Zigmond Request for Comments: 2838 WebTV Networks, Inc. Category: Informational M. Vickers Liberate Technologies, Inc. May 2000 Uniform Resource Identifiers for Television Broadcasts Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. RFC 2396]. This document describes a widely-implemented URI scheme to refer to such broadcasts.
ATVEF 1.1]. ITU RR]). Many modern television networks are not broadcasted over-the-air, but available only through cable or satellite subscriptions. The identifiers for these networks (such as the familiar "CNN" and "HBO") are not regulated at this time. In some countries, even over-the-air broadcasters use these sorts of identifiers, rather than call signs. Unfortunately, these two namespaces overlap, with most network identifiers also being valid call signs. Furthermore, network identifiers are not world unique, and many cases exist of name collisions. (For example, both the Australian Broadcast Corporation and the American Broadcasting Company identify themselves as "ABC".) In order to ensure uniqueness, the "tv:" scheme uses DNS-style identifiers for all broadcast streams. Because these build on the existing registration system for DNS hostname, all name collisions can be resolved through the existing DNS dispute resolution processes.
In the simplest form, domain names themselves are used as broadcast identifiers. For example: tv:abc.com the American Broadcast Company tv:abc.co.au the Australian Broadcast Corporation In some cases, networks have multiple broadcast streams that need to be distinguished. This is also handled in DNS style: tv:east.hbo.com HBO East tv:west.hbo.com HBO West It is important to note that these DNS-style identifiers need not match real hostnames; they should not be resolved to IP addresses using DNS. Thus, using the terms as defined in RFC 2396, the "tv:" scheme is a Uniform Resource Identifier and not a Uniform Resource Locator. In order to support these identifiers in a "tv:" URI, a receiver must implement a means to map known identifiers to frequencies. The nature of this map and the way in which it is used are currently browser- and device-specific and are beyond the scope of this document. In this way, the "tv:" scheme is somewhat analogous to the "news:" and "file:" schemes in : it merely names a television broadcast signal but assumes that the local browser has some means for actually retrieving that signal on the local device. A variety of software systems currently provide device-specific mappings from such identifiers to specific channel numbers or directly to frequencies. These systems can be incorporated into television sets or set-top boxes to facilitate the interpretation of television URIs by the client device.
RFC 2396]. Furthermore, the definition of dns-identifier is identical to the definition of hostname in RFC 2396, and is case-insensitive. RFC 2396]. It is possible that the mere act of viewing a television broadcast signal may cause costs to be incurred to the viewer in some instances (e.g., "pay-per-view" movies and events). Any software that uses this URI scheme to allow automatic tuning of a client device to a particular television broadcast signal should alert users before performing actions that may incur costs to the user. [RFC 2396] Berners T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [ATVEF 1.1] Advanced Television Enhancement Forum, "Advanced Television Enhancement Forum Specification Version 1.1r26," February 1999. http://www.atvef.com/library/spec1_1a.html
[ITU RR] International Telecommunications Union, "Radio Regulations," 1998. See especially Article S19, "Identification of stations," and Appendix S42, "Table of allocation of international call sign series."
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